Holocene stratigraphy of Cobweb Swamp, a Maya wetland in northern Belize
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We investigated the soils and sediments of Cobweb Swamp, adjacent to the archaeological site of Colha in northern Belize, to adumbrate landscape evolution and the impact of the ancient Maya on a tropical palustrine wetland. The Cobweb section exposes a complex and dynamically evolving landscape, with a rich interplay between natural and human forces. The Cobweb depression probably formed as a karstic doline or polje in interbedded limestone and marl of late Tertiary or Pleistocene age. During the latest Pleistocene, a terrestrial marsh covered most of the depression. Slope wash and colluviation from adjacent slopes impacted the depression during the early Holocene, possibly in response to a drier and cooler climate reported to have occurred in the region during this time. After ca. 5600 B.P., the Cobweb depression was affected by relatively rapidly rising sea levels in the area, and a brackish lagoon filled the basin. By 4800 B.P., a peat filled in the lagoon, probably because precipitation of a marl in the lagoon coupled with decreasing rates of sea-level rise enabled emergent vegetation to encroach the shallowing waters. Humans first began to affect the landscape when this peat was at the surface. Massive deforestation, resulting in increased runoff and rising water levels, is the most likely explanation for a fresh-water lagoon that again inundated the Cobweb depression between 3400 and 500 B.P. The Maya Clay was deposited on the edge of this lagoon as the result of upland erosion, almost as soon as deforestation began, but the bulk of the deposit was coincident with the sudden collapse of the Classic Maya civilization ca. 1000 B.P., suggesting that significant environmental degradation was associated with the demise of the Classic Maya. Peat began to fill the Cobweb lagoon sometime before 500 B.P., probably the result of shallower water levels from decreasing runoff resulting from reforestation after abandonment by the Maya.
